How to duplicate an object with rig and animation?
You can use Blender's group linking system:


select both your mesh and its armature
hit CTRL + G to put them in a group (and eventually hit F6 to name that group)
If you need a clean scene, you can create a new empty scene (in the "info" toolbar (at the top of the default UI layout), the + button)
hit SHIFT + A and select "Group instance", then choose the group you just created
repeat the last step as many of time you need duplicates
play the animation, all the groups should be animated the same.


If you need one group instance to play the animation mirrored, you can scale it on X and Y axis with value -1 (S > SHIFT+Z > -1)